1. Field of the Invention
This invention relates to a laminar structure for administering a chemical at a controlled release rate and more particularly, to a structure comprising a layer having therein a first chemical portion and a second chemical portion where the portions comprise a mixture of different transport concentration modes of the chemical.
2. Description of the Prior Art
Controlled drug release devices, in the form of discs, bandages, patches, etc. are presently being employed to treat various diseases. These devices are employed to transdermally administer drugs such as scopolamine, clonidine and nitroglycerin. These devices typically contain a single active drug component dispersed or dissolved in a fluid such as mineral oil, silicone fluid, water, glycerin, etc. and incorporated into a reservoir using a controlled release mechanism, such as for example gel-like matrices fabricated from a combination of polymers and a rate controlling microporous polypropylene membrane, a microporous ethylene-vinyl acetate copolymer membrane, and a micro-sealed silicone matrix. In this regard, the following U.S. Pat. Nos. 3,797,494; 4,294,820; 4,201,211; 3,742,951; 4,336,243; 4,438,139; 4,031,894; 4,436,741; 3,731,683; 3,464,413; 3,426,754; 3,598,123; 3,972,995 describe such time release devices or systems.
Existing time release medicament devices which employ polymeric matrices have as a major drawback the fact that the release rate of active drug or chemical is diminished with time. Accordingly, a constant rate drug delivery system over an extended time period is desired which does not employ (1) a rate-controlling membrane between the drug containing matrix and the skin contact area of the patient, (2) microcapsules for holding and/or releasing the active drug or (3) hydrophilic or hydrophobic solvent systems for dissolving or suspending the drug to be delivered.